This ensures a year-round water supply to hundreds of millions of people in the Indian subcontinent and China.

The WWF report is published in the run-up to two meetings in London on climate change organised by the UK as current head of the G8 group of industrialised nations.

The gatherings, a ministerial roundtable of the 20 largest energy using economies in the world, and then a G8 meeting of development and environment ministers focusing on climate change, take place this week.

A study commissioned by WWF shows that dangerous levels of climate change could be reached in just over 20 years and that if nothing is done, the Earth will have warmed by 2°C above pre-industrial levels by some time between 2026 and 2060.

As glacier water flows dwindle, the energy potential of hydroelectric power will decrease, causing problems for industry, as well as agriculture, as reduced irrigation means lower crop yields, WWF says.

The environmental watchdog's report shows that three of Nepal's snow-fed rivers have shown declining discharge. Nepal has an annual average temperature rise of 0.06°C a year.

In northwest China, the Qinghai Plateau's wetlands have seen declining lake water levels, lake shrinkage, the absence of water flow in rivers and streams and the degradation of swamp wetlands, the report says.

India's Gangotri glacier, which supports one of India's largest river basins, is meanwhile receding at an average rate of 23 metres a year.